This invention relates in general to annular seal assemblies that resiliently engage the outer surfaces of shafts to prevent the passage of oil or other liquids therethrough. In particular, this invention relates to an improved structure and method of manufacturing an outer surface of such a shaft that minimizes leakage through the annular seal assembly when such shaft is rotated or otherwise moved relative thereto during use.
In many mechanical devices, two or more components are supported within a housing for movement relative to one another. It is well known that when any of these components engage one another during such relative movement, friction causes undesirable heat and wear to occur. To minimize the adverse effects of such friction, it is often desirable to provide a quantity of lubricant within the housing. By providing the lubricant on the engaging surfaces of the relatively moving components, the amount of friction that is generated during operation is reduced, thereby prolonging the useful lifespan of the device.
In some instances, it is necessary or desirable that one or more of the components extend outwardly from the housing of the device so as to engage or be engaged by an ancillary structure. For example, a cylindrical shaft may extend outwardly through a bore formed through the housing of the device so as to rotatably drive (or, alternatively, be rotatably driven by) the ancillary structure. In these instances, it is usually necessary to provide a seal between the housing and the shaft to retain the lubricant within the housing and to prevent dirt, water, and other contaminants from entering into the housing.
One well known structure for providing such a seal is an annular seal assembly. A typical annular seal assembly includes a rigid outer annular case having a resilient inner seal secured thereto. The rigid outer case is press fit within the bore formed through the housing of the device and provides a fluid-tight seal therebetween. The resilient inner seal includes a flexible lip portion that extends radially inwardly into sealing engagement with an outer surface of the shaft extending therethrough. If desired, a garter spring or other biasing mechanism can be provided to positively urge the flexible lip portion into sealing engagement with the outer surface of the shaft. In either event, the lip portion of the resilient inner seal engages the outer surface of the shaft to retain the lubricant within the housing and to prevent dirt, water, and other contaminants from entering into the housing, regardless of movement of the shaft (such as rotational or reciprocating movement) relative to the housing.
Ideally, the outer circumferential surface of the shaft would be formed having a plurality of relatively small irregularities that are evenly distributed thereabout. Such irregularities can be characterized as being either relatively higher portions (i.e., small hills in the outer circumferential surface of the shaft that extend above the desired outer diameter thereof) or relatively lower portions (i.e., small valleys in the outer circumferential surface of the shaft that extend below the desired outer diameter thereof). The presence of these hills and valleys is desirable because small amounts of lubricant are trapped in the valleys during use. The trapped lubricant reduces the amount of friction between the outer circumferential surface of the shaft and the flexible lip portion of the resilient inner seal engaged therewith. So long as such surface irregularities are relatively small in size and sufficiently evenly distributed across the outer circumferential surface of the shaft, then their presence will not likely adversely affect the operation of the annular seal assembly.
However, as a practical matter, the processes used to manufacture the shaft have not been sufficiently controlled in the past to insure that size and distribution of these surface irregularities would not adversely affect the operation of the annular seal assembly. Thus, the outer circumferential surface of the shaft is rarely formed having such relatively small and evenly distributed surface irregularities. On the contrary, the outer circumferential surface of the shaft is usually formed having irregularities that are sized and distributed in such a manner as to adversely affect the ability of the annular seal assembly to prevent leakage therethrough. When this occurs, the shaft is said to possess a preferential lead. A preferential lead present when the irregularities formed on the outer circumferential surface of the shaft are arranged in such a manner as to draw or pump liquid past the engaging surfaces of the shaft and the annular seal assembly when the shaft is moved during use, similar to a helical thread being formed in the outer circumferential surface of the shaft.
Traditionally, the solution to the presence of a preferential lead on a shaft has been to test the shaft to determine if such a preferential lead exists and, if so, determine the direction of such preferential lead (i.e., from left end to right end or right end to left end). If the shaft possesses a preferential lead of sufficient magnitude, then it must be installed in the device in an orientation that causes the preferential lead to draw or pump liquid back within the housing when the shaft is moved during use. Otherwise, it is likely that leakage will occur through the annular seal assembly during use. On the other hand, if the shaft possesses no preferential lead (or a sufficiently small preferential lead), then it can be installed in the device in either orientation relative to the housing and the annular seal assembly. Although effective, this testing procedure has been found to be time consuming and inefficient. Thus, it would be desirable to provide an improved structure and method of manufacturing an outer surface of such a shaft that avoids the creation of a preferential lead and thereby minimizes leakage through the annular seal assembly when such shaft is rotated or otherwise moved relative thereto during use.
This invention relates to an improved structure and method of manufacturing an outer surface of such a shaft that avoids the creation of a preferential lead and thereby minimizes leakage through the annular seal assembly when such shaft is rotated or otherwise moved relative thereto during use. The outer circumferential surface of the shaft is formed having a plurality of relatively small irregularities that are evenly distributed thereabout. Such irregularities may be defined by relatively higher portions and relatively lower portions that are formed in an intersecting, cross hatched pattern or in a circumferentially extending undulating or oscillating pattern. To form the cross hatched pattern, an apparatus can be operated to engage the outer circumferential surface of the shaft in two sequential passes in opposite axial directions while the shaft is being rotated. To form the undulating pattern, an apparatus can be operated to engage the outer circumferential surface of the shaft in an axially reciprocating manner while the shaft is being rotated. By varying the feed rate of the apparatus, the rotational speed of the shaft, and the magnitude of the force applied by the apparatus against the outer circumferential surface of the shaft, the size, shape, and depth of the surface irregularities can be varied as desired.